if 0 {[Richard Suchenwirth] - 2004-06-04 - In the [Tcl chatroom] I saw a
request for finding the position of a sublist in a list, so that
 lsubl {a b c a d e} {a d}
would return 3. A number of famous algorithms (only not to me) were
mentioned: Knuth-Morris-Pratt, Rabin-Karp, Boyer-Moore-Gosper. I'm more
the practical kind of guy, so I decided just to give it a try, like
this:
   * Find all possible starting positions of the sublist
   * Check whether they comply; return the first to match, or -1 if none
Here's my code:
}
 proc lsubl {list sublist} {
    set sl [llength $sublist]
    if {!$sl} {return 0}
    foreach i [lsearch -all $list [lindex $sublist 0]] {
        if {[lrange $list $i [expr {$i+$sl-1}]] eq $sublist} {
            return $i
        }
    }
    return -1
 }
#Tests:
 proc ? {c e} {catch $c r; if {$r ne $e} {puts "$c->$r, expected $e"}}

 ? {lsubl {a b c a d e} {a d}}  3
 ? {lsubl {a b c a d e} {a b}}  0
 ? {lsubl {a b c a d e} {a f}} -1
 ? {lsubl {a b c a d e} {}}     0 ;# empty list is everybody's sublist

if 0 {Could some algorithm-knowers comment, please? :)

[FW]: Hmm, algorithms for this task are probably so many many because it's pretty much the same idea as finding the index of a substring, which of course is very common.  For your one-char items ''proc lsubs {list sublist} {string first [[join $sublist ""]] [[join $list ""]]}'' works.
- [RS]ever indeed - thanks! (But the question was of course for general list elements...)
----
[Arts and crafts of Tcl-Tk programming]
}